[Android Central Question]

Initially, since I got the note 8 I was very cautious about the charging cycles. I let it charge upto 85% and let it drop to 25% and not below. I let it fall to 5% every 15 days and charge it to a 100%. Recently, I let my note 8 fall below 25% and once it touched 15%, the battery started discharging rapidly. Lost 10% in 3mins and dies at around 6%. I only use wifi, no smart gestures are enabled, I don't sync stuff, I even calibrated the battery, but nothing worked.

[belodion]

It could need a new battery.

[Rukbat]

The schedule you followed, not fully charging it, regularly discharging it to 25%, letting it fall to 5% twice a month, is killing the battery.

First, there's no memory effect in lithium batteries, so you don't have to discharge it to "remove the memory".

Second, lithium batteries are not deep discharge batteries, you should never let them drop below 40% (50% is a better charge point for longer life).

I don't know what you mean by "calibrated the battery" - the file you have to change to do that is a system file, so the phone would have to be rooted to calibrate the battery.

As Belodion said, you probably need a new battery - and with the new "customer can't be trusted to replace the battery" meme in cellphones, that means sending the phone to Samsung (or at least giving it to a reputable repair shop), which will most likely mean a factory reset. (That way, you can't accuse the repair shop [or Samsung] of stealing your data.)